Following ways have been used for searching information from a data group like retrieval of office document in an industry, document retrieval from an electronic library, and Web page browsing in a WWW (World Wide Web) that is linked.
a. Use of Search Engine
By using a full-text search technology that is used for text information, attributes and outline of title of data that matches with a keyword that is input by a user are listed up in an order of degree of matching and is provided to the user. The user selects data from the list that matches with his requirement and browses contents of the data.
b. Use of Category
By some way, a data group is classified according to levels in categories and the user searches information by using the category levels.
c. Use of Link
Information that matches with the user's requirement is searched by tracing a link from data that is selected by some way.
However in ‘a’ mentioned above, sometimes the number of search results that are provided by a search engine is enormous and the order in which the search results are provided does not match with the user's requirement. In such case, it is difficult for the user to get the desired information. Sometimes, sufficient information cannot be obtained by browsing a single data. In such case, it is difficult to judge an order in which a plurality of data that is listed up is to be browsed. Sometimes, data that has to be browsed may not be even listed up.
In ‘b’ mentioned above, when the classification in categories does not match with the user's requirement, it is difficult for the user to get the desired information. Moreover, similarly as in ‘a’ mentioned above, when sufficient information cannot be obtained by browsing a single data, it causes a problem.
In ‘c’ mentioned above, when the link is not proper, there is a possibility of browsing unnecessary data. Moreover, while tracing the link, the search may go astray due to inability to return to an original data etc.
To obtain the desired information efficiently from the data group that is linked mutually, it is desirable to start from suitable data and go on browsing related data in a suitable order. When a wrong order is followed, it is desirable to return to the original data or to data that is browsed earlier. For this, it is necessary to solve the following issues (problems) (1) to (4).                (1) How to decide from which data to start?        (2) How to decide as to which data has to be browsed next?        (3) How to identify position of data that is browsed or data that is being browsed in the overall data that has to be browsed.        (4) How to visualize efficiently, a link relationship between data.        
Therefore, an object of the present invention is to provide an information navigation system in which these issues are solved.